Couple of Quick Qs about MCR games:

jonathan1138

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Hi - Have a few hopefully quick questions regarding Bally / MCR games (in this case this EDOT):

-- On the MCR Power supply board, there is a 3/8 fuse (the manual calls for 3/8). I keep blowing that. I upped it to .5 fuse, game runs a little longer, but still breaks the fuse within a minute or so. What would the harm be by using a 1 amp fuse? What exactly is this fuse protecting? I still plan to solve the fuse blowing, i think it maybe the diodes on the xformer... just wondering about 1 amp usage.

-- What do the dual amp boards do? There are two of them in the cab.

--I hear of people cutting the "Purple wire" on the power supply - VBATT line - what is that exactly?
 
Hi - Have a few hopefully quick questions regarding Bally / MCR games (in this case this EDOT):

-- On the MCR Power supply board, there is a 3/8 fuse (the manual calls for 3/8). I keep blowing that. I upped it to .5 fuse, game runs a little longer, but still breaks the fuse within a minute or so. What would the harm be by using a 1 amp fuse? What exactly is this fuse protecting? I still plan to solve the fuse blowing, i think it maybe the diodes on the xformer... just wondering about 1 amp usage.

-- What do the dual amp boards do? There are two of them in the cab.

--I hear of people cutting the "Purple wire" on the power supply - VBATT line - what is that exactly?

Does the fuse still blow with the motherboard unplugged?

Purple wire is the reset signal. When the reset circuit is bad, the motherboard won't boot. Some games do not need the reset signal....so, cutting the purple wire will actually enable them to boot. Now, some MCR games will not boot with the reset signal floating. They need it and it has to be working properly. A lot of people saying "cut the pruple wire" are just repeating what they've been told/read online/etc....and that might not be the best advise.

VBATT is battery voltage.

Edward
 
-- On the MCR Power supply board, there is a 3/8 fuse (the manual calls for 3/8). I keep blowing that. I upped it to .5 fuse, game runs a little longer, but still breaks the fuse within a minute or so. What would the harm be by using a 1 amp fuse? What exactly is this fuse protecting? I still plan to solve the fuse blowing, i think it maybe the diodes on the xformer... just wondering about 1 amp usage.
My copy of the schematic calls for a slo-blo. Before you dive-in, make sure you haven't installed a fast blow.

The fuse is on the power supply, or on the transformer assembly? Why would you think diodes on the transformer assembly could cause this? Fuse F1 is the only 3/8 amp fuse that I see and it limits the unregulated input of regulator U2 and the booster transistors. I'd be diagnosing the +5v power supply circuit. Most of these parts are included in a rebuild kit.

-- What do the dual amp boards do? There are two of them in the cab.
Stereo audio amplifier.

--I hear of people cutting the "Purple wire" on the power supply - VBATT line - what is that exactly?
Check your schematic. J4-1 VBATT is grey, it's battery backup power to save high scores. J4-15 is violet, it's a power-on reset signal that tells the game to run once the power has stabilized. It also detects momentary power cut-outs and forces the game to reset. People who are unable to fix the electronics will sometimes cut that wire, disabling the power-on reset feature.
 
Elutz,

There are several boards on this game - light control boards (2), Lamp Relay boards (2), Dual amp boards (2), -5 volt board (1), the S&T board for speech (1) and the main PCB (3 stack). Do you mean Main PCB as the mother board?

With all plugged in EXCEPT the S&t board and the Main PCB - no blown fuse at F1 on the PS, 5.10 volts.....good!

When i plug in Others + S&T (but no Main PCB) i get 3.9 volts. Fuse gets "cloudy".

When i plug in others + Main PCB (no S&T) i get 1.3 volts, fuse blows.

All of them together - dead (0 volts) with blown fuse.

CD Jump suggests that the xformer diode(s) need replacing - i am waiting for them in the mail. Hoping thats it.

Any other advice is helpful.
 
Joey,

The PS was rebuilt by CDJump last week, so we are trusting its working for now.

I wasnt able to get the game to even boot until i replaced the xformer caps (the two large ones) - at least now, i got Tron on screen shortly before fuse blows (one time event, cant get him back).

While under the xformer, i *THINK* (diode was in circuit so hard to tell) one of the diodes was testing wrong, so that may be it. I hope it is - i will know for sure once i clip it / test it again....

Yes, using slo blos only (tried 3/8 slo blo, doesnt last more than a few seconds - half amp slos last a little longer, maybe a minute or so).
 
Elutz,

There are several boards on this game - light control boards (2), Lamp Relay boards (2), Dual amp boards (2), -5 volt board (1), the S&T board for speech (1) and the main PCB (3 stack). Do you mean Main PCB as the mother board?

With all plugged in EXCEPT the S&t board and the Main PCB - no blown fuse at F1 on the PS, 5.10 volts.....good!

When i plug in Others + S&T (but no Main PCB) i get 3.9 volts. Fuse gets "cloudy".

When i plug in others + Main PCB (no S&T) i get 1.3 volts, fuse blows.

All of them together - dead (0 volts) with blown fuse.

CD Jump suggests that the xformer diode(s) need replacing - i am waiting for them in the mail. Hoping thats it.

Any other advice is helpful.

Oops sorry.....yes, for motherboard....I was speaking of the main 3-board stack. The transformer assembly diodes should all test the same....so, if one test differently.....it's worth investigating. If you tested it "in circuit", something else could cause a different reading. When in doubt, remove and retest.

I agree with Joey, it would be strange for any issues associated with the transformer assembly to blow the fuse on the power supply board. The transformer assembly has it's own fuses, but.......never say never. Are the other fuses the proper size?....no 20 amp fuse stuck where a 5 amp goes?:D.

The few times I've ever had the power supply fuse blow was because of issues on the power supply board. Both times it was one of those tantalum caps. Do you have another MCR game you could toss the power supply board into and double check it's operation?

Edward
 
Elutz,

No problem. All fuses on xformer and ps are compliant.

Yeah, i wish i had another PS now. I just sold two on ebay last month - of course. A "somewhat" local buddy offered to stop over with a PS, but thats not gonna be for awhile.

I will change that diode on the xformer and see what happens. MJenison made some suggestions (a bit over my head) on my other thread, so i will look into that.

Really hoping its a bad diode. It could be as that rectifies voltage up to the board. Maybe tonight i can get it installed.
 
Ah, so this thread has more information :)

So, you've got basically a known good board (checked by CDJump) and a known good PS (rebuilt by CDJump).

Did you try disconnecting all other cables from the PCB, only attaching the video cable and the power connector to the PCB, with all other boards disconnected?
 
While under the xformer, i *THINK* (diode was in circuit so hard to tell) one of the diodes was testing wrong, so that may be it. I hope it is - i will know for sure once i clip it / test it again....
That's fairly easy to check. The transformer assembly outputs unregulated +15v / +8v DC. Start with stuff disconnected. Measure DC coming off the transformer assembly and expect around +15 / +8. Measure AC and expect none since you installed new caps. Do the same with your power supply loaded, when you described seeing 3.9v. Make sure the unregulated voltage doesn't act differently (start dipping, producing AC). Measure at a few different points like closer to the transformer, closer to the regulator. Previous battery acid damage can leave you with faulty connectors and faulty traces and could cause a confusing voltage/current drop.

If you see problems with the +15 / +8 then maybe your transformer diodes are faulty. If those voltages look fine then forget about the transformer and focus on your power supply board. Like ELutz said, try to double check your assumptions and retest the power supply board in another machine.

I wasnt able to get the game to even boot until i replaced the xformer caps (the two large ones) - at least now, i got Tron on screen shortly before fuse blows (one time event, cant get him back).
Brand new caps can smooth-out the voltage from a faulty rectifier enough to cover-up some problems. Measure the unregulated voltage as described above to prove if it's good or bad.

The PS was rebuilt by CDJump last week, so we are trusting its working for now.
It tested working in another MCR game? The +15v through that fuse feeds the regulator and the power pre-amplifiers. I don't know why those three parts would consume an excessive amount of current unless they're damaged. Wouldn't expect that fuse to blow even with a excessive current draw on +5v. Maybe you have low/faulty unregulated +15 / +8 off the transformer? Will be interesting to hear the answers for the tests above.
 
Ah, so this thread has more information :)

So, you've got basically a known good board (checked by CDJump) and a known good PS (rebuilt by CDJump).

Did you try disconnecting all other cables from the PCB, only attaching the video cable and the power connector to the PCB, with all other boards disconnected?


Yes - more information here! Was just starting this for new questions, but they are all related.

I disconnected everything, 5 volts steady. I "ramp" up my connections (power off between plug ins) to the other PCBs. I am fine UNTIL i get to sound board (drops to 3.9, fuse gets cloudy) or main PCB (fuse oranges up, blows).

On the Main PCB only (everything else disconnected) - videa cable and power cable (left side big connector on the PCB) - still blow the fuse.
 
Joey -

Yes, CD Jump ran this PS on his SH for a day or so. Thank you very much for the tests to try - looking forward to doing that tonight.

Last night, i found this thread by SuperGunGuru (he looks like Mcguyver a little bit):

http://forums.arcade-museum.com/showthread.php?t=46854

Sounds like the exact problem right down to the glowing orange fuse. He was right where i am now - he opted for a Arcadeshop switcher at that point. I cant do that on an EDOT without "hacking" the wiring since the lamp boards / S&T dont interact with the adapter out of the box.

His only next step were those diodes (he had a good PS it seems, good boards, new caps, what else could it be?) -

More to follow after i run those tests (and again, get those diodes in stock).
 
I have an EDOT. Hookup everything but don't plug in the PS board. What resistance do you see in the wiring harness to the game between the gnd connection and the +5VDC?
 
I have an EDOT. Hookup everything but don't plug in the PS board. What resistance do you see in the wiring harness to the game between the gnd connection and the +5VDC?


Will try as soon as i get home tonight (along with Joey's notes...)

MJenison - if i can clarify: Dont plug in the PS board - Meaning:

Dont plug in J6 / J3 (coming off the Xformer into the PS)
AND / OR
Dont plug in J4/J5 (going out from the PS to the PCBs)


As for the Gnd and +5VDC - do you mean the Gnd pin on the cab (outlet plug?) and +5VDC point after the PS (like at the cap i've mean measuring it at, C106 i think)....

Thanks again for any help.
 
The latest. Installed 4 new MR1120 Diodes on the power prick (thats intentional naming).

Start the game with nothing plugged in except PS, getting 5v and 12v. Add everything else, i blow F3 on the xformer (5 amp slo blo).

Ok- different results now i guess. Unplug all PCBs EXCEPT main game board (J1 + all others). Game plays! Wow. No sound or lights, but it plays. Progress?

No. After ten minutes, both F3 on the xformer and F1 on PS blow.

More digging to do i guess.
 
I think the mjenison suggestion makes sense to check resistance. It would be nicer to compare unregulated +8v current but that's not quite as easy of a test to setup.
 
Ok.... here is the latest conclusion, thanks to some help from CDJump. MJenison and Joey touched upon it to - resistance in the harness.

I checked my connectors - for the most part they look good, but i notice a little green acid damage to the J4 / J5 plugs off the PS. This could be it..... the big one. Hoping it is. I happen to have (i think) Bob Roberts connection rebuild kit on hand, so will try that tomorrow evening. I sure hope this is the one.

I think the diode replacement / new caps prolonged the life before the draw kicks in (i was at 1 minute before a blow, now i am up to 10!).

MJenison - if you can - please let me know where i should measure from (you mentioned 5vdc to ground - i wasnt sure which exact points?) - i would love to compare resistance notes.

Thanks.
 
I've seen battery corrosion eat through that entire harness bit.....transformer assembly connections to the power supply connectors. Check both ends of that harness bit.

Edward
 
Ok here is where i am at.... Rebuilt the J4 / J5 connectors that come out of the PS. Slightly better results - F5 fuse on the xformer is not showing signs of burning after running the cab for 5 minutes, nor is the PS fuse.

BUT i am still clouding up / close to blowing fuse F4 on the transformer assembly, so something still must be pulling.

Looking at these wires now - the audio shielded wires - they are somewhat flimsy and the black strand part is mostly exposed (i think this is common from the factory). Still Looking for any other signs of shorts in the wiring... am i on the right track? Is there something else i should be studying?
 
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